Polychlorinated biphenyls (PCBs) are a group of highly refractory chlorinated aromatic compounds posing major environmental and health problems. Efficient treatment technologies which destroy PCBs without producing dangerous degradation products are essential to minimize potential human health problems. Remedial anaerobic biodegradation offers considerable promise as a means of treating contaminated sediments, soils and waters, since anaerobic microbial consortia have been shown to reductively dechlorinate PCBs in sediments. A three-year laboratory study is proposed to establish and maximize PCB degradation in a laboratory-scale bioreactor. The ultimate goal of this research is to design an "in-situ" bioremediation process applicable to contaminated sediments, soils and leachate from the Massena Inactive Hazardous Waste Sites (MIHWS). Our three-year research goals are: 1) to determine and maximize the relative rates of dechlorination of a complex PCB leachate from the MIHWS in a 10 L recycling-upflow anaerobic sludge blanket-anaerobic filter (R-UASB-AF) bioreactor; 2) to design and operate an anaerobic laboratory-scale recycling-upflow fixed bed (R-UFB) slurry (high-solids) reactor to assess the relative rate of dechlorination ont he MIHWS soils and sediments; 3) to assess design characteristics for an on- site pilot scale anaerobic treatment system to bioremediate the MIHWS soils, leachates and St. Lawrence riverine sediments.